1. The discharge in myelinated afferent fibres innervating hairs in anaesthetized cats and rabbits, dissected from the saphenous nerve, was recorded during controlled movements of the hairs.2. Three types of rapidly adapting afferent unit were found and they innervated three kinds of hair follicle-down hair, guard hair and tylotrich.3. The down hair units had low thresholds (critical slopes) and some of the guard hairs had the highest thresholds and least sensitivity to displacement.4. There was a good fit to a power function for the relation between velocity of displacement of a hair and the frequency of discharge in the corresponding afferent fibre.5. It is concluded that the rapidly adapting hair follicle receptors can function as efficient exact movement detectors.6. Tylotrich follicles were often associated with touch corpuscles, but there was independent innervation of the rapidly adapting tylotrich follicle receptors and the slowly adapting touch corpuscle receptors.7. The conduction velocities of large populations of myelinated cutaneous axons innervating cutaneous mechanoreceptors were measured in cats and rabbits.